1. Field of the Invention
The invention relates to a solution as well as to a process for metallizing non-conductors using conductive polymers.
It is known to process non-conductive surfaces in the following steps:
a) Process with a solution containing suspended or solute oxidation agents, so that an oxidation agent is adsorbed or created on the non-conductive surface. PA1 b) Process with a solution containing at least one aromatic compound, which can be converted through oxidation into a conductive polymer, and at least one water-soluble polymer. PA1 c) Metallize through electroplating. PA1 pre-swelling in organic solvents PA1 etching with permanganate PA1 pyrrolic polymerization in acid PA1 metallization. PA1 polyethyleneimine PA1 poly(N-methyl-ethyleneimine), PA1 polyvinyl alcohol PA1 polyethylene oxide PA1 polypropylene oxide PA1 copolymer of polyethylene oxide and polypropylene oxide PA1 polyacrylic amide PA1 poly-1-vinylpyrrolidone PA1 poly(2-vinylpyridine) PA1 poly(4-vinylpyridine) PA1 polyethylene glycol PA1 poly(N-methyl-N-vinylimidazolium methosulfate) PA1 polyamine sulfones PA1 poly(N,N-dimethyl-3,5-dimethylene-piperidinium chloride) PA1 poly((3-chlor-2-hydroxy propyl)-1-imidazole) PA1 poly(N,N-diallyldimethylammonia chloride). PA1 1. The non-conductor surface is pre-treated with the objective of producing or adsorbing oxidation agent on the non-conductor surface. PA1 2. The pre-treated substrate material is treated with the solution according to the invention, which contains the water-soluble polymers and the aromatics, which are polymerized to an intrinsically conductive polymer through oxidation with the oxidation agent formed in Step 1 on the non-conductor surface. A conductive layer is thereby formed. PA1 3. The previously insulating and now conducting areas are metallized in an electroplating bath.
2. Discussion of the Prior Art
In DE 38 06 884 C1 and EP 0 413 109 A2, processes of this type using conductive polymers for the metallization of non-conductors are described. What is crucial in both processes is that the otherwise necessary intermediate step of chemical metallization may be omitted and that electroplating is achieved in a shorter process.
The processes described above have technical disadvantages, however. According to DE 38 06 884 C1, the monomer needed to produce the conductive polymer is adsorbed on brownstone, and the acid required for polymerization is not added until after this has occurred. This sequence results in the quantity of monomer being limited both by its adsorption capacity on brownstone and by the quantity of brownstone on the non-conductive surface. This can lead either to insufficient polymerization through oxidation of the monomer or to over-oxidation, so that the requisite process reliability is not guaranteed.
In the process described in DE 38 06 884 C1, the post-treatment step with acid constitutes the essential step in polymerizing the monomer into the conductive polymer, because an acid is needed along with the oxidation agent for the chemical expression of a conductive polymer. This sequence of steps results in a longer process. Furthermore, in this process, volatile solvents are used together with the volatile pyrrole. This pollutes the environment and impairs occupational safety, because in order to achieve adequate polymerization a high concentration of the monomer must be used in the solution, meaning that solubilizers must be added to the solution when water is used as the preferred solvent.
In contrast, the process according to EP 0 413 109 A2 uses already finished polyaniline, which is applied by coating to the non-conductive surface. In addition to the requisite prior synthesis of the polyaniline, the selectivity of the process and the not always adequate adhesion of the polymer layer to the non-conductive surface constitute significant problems of this process.
In DE 39 39 676 A1 and EP 0 457 180 A2, a process for metallization is described which is based on the process steps:
This process does not use the oxidative spectrum of the permanganate to produce sufficient oxidation agent; an additional pre-treatment step with organic solvents is required. The use of N-methylpyrrolidone in the swelling step is disadvantageous because of the limited retention time of the swelling bath, since the compound has only low acid stability. The temperatures specified in both documents for the pyrrolic polymerization bath are not optimal for an even conductive layer. In addition, the volatility of the solvent and the pyrrole used in these processes also presents a problem, because their emission from processing equipment pollutes the environment and reduces occupational safety.
In U.S. Pat. No. 4,617,228 a process is described for the impregnation of porous substrate materials, e.g., glass fiber fabric, in which a liquid pyrrole compound and a solution of a strong oxidation agent are brought into contact sequentially with the substrate material in the presence of a non-nucleophilic anion. Conductivity in the carrier material is attained through the precipitated conductive layer of conductive polymer. Neither further electroplating metallization of the conductive polymer layer nor electrical resistance values of the conductive polymer layer are disclosed, so that there is no way to tell whether a sufficient electroplating capability even exists.
In JP 63 125696 A, the plating of non-conductors using a chemically manufactured polypyrrole film and subsequent electroplating is described. The polyvinyl alcohol specified in this document serves as an impregnation agent and is added as a solvent in the function of a matrix for the organic conductor. Polymerization occurs in the condensed matrix of the impregnation agent polyvinyl alcohol. The in situ expression of the oxidation agent, which-like brownstone-adheres tightly to the non-conductive surface, is not described. As an example, the reaction of iron-Ill-chloride in a pre-generated matrix with pyrrole is described. The document also does not point to any solution for the problem of the volatility of the aromatic compound that can be oxidized to a conductive polymer.
In industrial use of these solutions, it has been shown that the aforementioned aromatic compounds, such as pyrrole, for example, have a relatively high vapor pressure, so that during longer operation black deposits are formed on any surfaces in the area of containers containing these solutions, arising from the smallest traces of acids, the atmospheric oxygen and the gaseous compound added thereto.
To prevent emission of the aromatic compounds, treatment solutions of this type are known to be used according to the prior art in closed units. However, this is complicated and expensive and, furthermore, economically feasible only when certain otherwise advantageous processing techniques can be used, for example, during the horizontal conveying of printed circuit boards during their through-hole plating.